Abstract
Acidification has widely led to mitigating measures including reduced emission of acidifying substances and, as in Sweden, the implementation of a substantial liming programme. Recent hydrochemical research has, however, shown that many freshwater systems, in particular in the northern part of the country, may be naturally acidic suggesting that liming may be unsuitable when taking economy and conservation into consideration. The present research project addresses in a new way the issue whether streams are largely naturally acidic. Our hypothesis predicts that, if this is the case, such systems should have organisms that are well adapted to acid conditions. A preliminary investigation has shown that both the taxonomic diversity of macroinvertebrates and the decomposition rate of leaf litter were indeed not lower in acid than circumneutral sites in the province of Västerbotten. These relationships are now being tested at a nationwide scale in streams. Responses in streams which are naturally acid but vary in the water’s levels of organic carbon and inorganic aluminium content, and in streams which are being limed, are studied in a similar way. We also plan to investigate common properties of tolerant species that may explain their prevalence in acid environments in series of experiments in the field and laboratory. Gaining such knowledge would be useful, for example to support ecological functions in streams impacted by anthropogenic acidification via species introductions.
Sweden